Search Images Maps Play YouTube News Gmail Drive More »
Sign in
Screen reader users: click this link for accessible mode. Accessible mode has the same essential features but works better with your reader.

Patents

  1. Advanced Patent Search
Publication numberUS6804406 B1
Publication typeGrant
Application numberUS 09/651,480
Publication dateOct 12, 2004
Filing dateAug 30, 2000
Priority dateAug 30, 2000
Fee statusLapsed
Also published asCN1244228C, CN1471792A, EP1314311A2, WO2002019704A2, WO2002019704A3
Publication number09651480, 651480, US 6804406 B1, US 6804406B1, US-B1-6804406, US6804406 B1, US6804406B1
InventorsChung-Jen Chen
Original AssigneeHoneywell International Inc.
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Electronic calibration for seamless tiled display using optical function generator
US 6804406 B1
Abstract
Calibrating a seamless tiled display image having multiple overlapping discrete images produced by multiple displays includes generating a display-to-screen spatial transformation function to reduce one or more undesirable geometric projector characteristics for each of the projectors used in the tiled display. Then the method includes generating a screen-to-camera spatial transformation function to reduce one or more undesirable geometric camera characteristics for each of the cameras used in capturing the tiled display images used in the calibration. Then the method requires generating a spatial luminance transformation function for effective color calibration for each of the display images in the tiled display. Then the method requires inputting a high-resolution image into a tiled display processor to form the tiled images of the tiled display, segmenting the inputted high-resolution image to form tiled images based on an array of images used in the tiled display, and pre-warping each of the segmented tiled images using the display-to-screen spatial transformation function to reduce the one or more non desirable geometric projector characteristics. Then the method requires applying an inverse of the spatial-luminance transformation function to each of the pre-warped images to effectively blend colors in the tiled display images.
Images(10)
Previous page
Next page
Claims(46)
What is claimed is:
1. A method of calibrating a seamless tiled display, comprising:
disposing a spatial filter in an image path;
displaying a subset of a first predetermined image on a screen using a projector;
capturing the subset of the displayed first predetermined image using a camera;
generating the rest of the first predetermined image not displayed on the screen due to the inclusion of the spatial filter in the image path using the captured subset of the displayed first predetermined image;
combining the captured subset of the first predetermined image with the generated rest of the first predetermined image to form a composite of the first predetermined image;
determining whether the formed composite of the first predetermined image has one or more undesirable projector characteristics; and
generating a display-to-screen spatial transformation function that can be applied to an input video signal of the projector to reduce the undesirable projector characteristics.
2. The method of claim 1, further comprising:
processing the input video signal using the display-to-screen spatial transformation function to provide a first transformed input video signal such that the one or more undesirable projector characteristics are reduced.
3. The method of claim 2, further comprising:
comparing the formed composite of the first pre-determined image with a predetermined expectation to determine whether the formed composite of the first pre-determined image has the one or more undesirable projector characteristics.
4. The method of claim 2, further comprising:
displaying an image on to the screen; and
manually adjusting the projector to have minimal spatial distortion in the displayed image.
5. The method of claim 4, wherein manually adjusting the projector comprises manually adjusting one or more projectors individually to obtain roughly a similar size, an overlap and a minimal spatial distortion of a displayed image.
6. The method of claim 4, wherein the capturing, determining and processing actions are periodically repeated.
7. The method of claim 1, wherein the first predetermined image is a dot pattern.
8. The method of claim 7, wherein generating the rest of the first predetermined image not displayed comprises using an extrapolation function to generate edge dots not displayed due to the disposing of the spatial filter in the image path.
9. The method of claim 8, wherein the extrapolating function comprises a least squares fit of a polynomial function.
10. The method of claim 9, wherein the extrapolating function is selected from the group consisting of a quadratic or a higher order polynomial function and a cubic-spline function.
11. The method of claim 1, which further comprising:
sequentially displaying flat field images of varying intensities using each of multiple projectors used in a tiled display system;
capturing displayed flat field images of varying intensities using the camera;
normalizing the captured flat field images with respect to highest and lowest flat field images for each of the multiple projectors;
determining a gamma-corrected linearized luminance at a center of the displayed flat field images of varying intensities for each of the projectors;
normalizing the flat field images with the determined gamma-corrected linearized luminance at the center of the displayed flat field images of varying intensities for each of the multiple projectors;
generating a spatial function that can be applied to simulate each of the normalized flat field images for each of the multiple projectors; and
determining a spatial-luminance transformation function using the spatial function for providing an effective color calibration for each of the multiple projectors.
12. The method of claim 11, wherein sequentially displaying the flat field images of varying intensities using each of the projectors further comprising:
defining gray scale levels of flat field images of varying intensities; and
inputting signals that correspond to the defined gray scale levels of the flat field images of varying intensities.
13. The method of claim 11, wherein determining the spatial-luminance transformation function further comprising:
applying the spatial function to predetermined sections of each of the flat field images;
determining a first set of coefficients of the spatial function for each of the predetermined sections of each of the flat field images;
generating the spatial-luminance transformation function that can simulate the determined first set of coefficients for each section of the predetermined sections of the normalized flat field images; and
determining a second set of coefficients for the first set of coefficients that will effectively blend colors in the tiled displays.
14. The method of claim 11, wherein the spatial-luminance transformation function is a quadratic or a higher order polynomial function.
15. The method of claim 11, wherein the flat field of varying intensities comprises flat field images of monochrome, red, green and blue colors of varying gray scales.
16. The method of claim 11, which further comprises:
displaying a predetermined template on to the screen;
capturing an image of the displayed predetermined template using the camera;
determining whether the captured image has one or more undesirable camera characteristics;
removing the predetermined template from the screen; and
generating a screen-to-camera spatial transformation function that can be applied to the images captured by the camera to correct for the one or more undesirable camera characteristics.
17. The method of claim 16, further comprising:
applying the screen-to-camera spatial transformation function to the captured subset of the displayed first predetermined image to reduce the one or more undesirable camera characteristics.
18. The method of claim 16, further comprising:
comparing the captured image with a predetermined expectation template to determine whether the captured image has the one or more undesirable camera characteristics.
19. The method of claim 16, wherein displaying a predetermined template on the screen comprises disposing a physical predetermined template on to the screen.
20. The method of claim 19, wherein the predetermined template is a dot pattern.
21. The method of claim 16, further comprising:
segmenting a high-resolution image to form tiled images based on an array of images in the tiled display system;
pre-warping each of the segmented tiled images; and
applying the spatial-luminance transformation function to each of the pre-warped tiled images to blend colors in the tiled display images.
22. The method of claim 21, wherein segmenting a high-resolution image further comprising:
inputting the high-resolution image;
segmenting the high-resolution image to form the tiled images based on the array of images in the tiled display;
adding a predetermined overlapping region to each of the segmented images; and
applying a ramping function to the overlapping region of each of the segmented images to ensure a correct proportion of color luminance mix in the overlapping region.
23. The method of claim 21, wherein pre-warping each of the segmented tiled images further comprising:
processing each of the segmented tiled images using the display-to-screen spatial transformation function to provide a first transformed input video signal to each of the projectors to reduce one or more undesirable projector characteristics.
24. The method of claim 21, wherein applying an inverse of the spatial-luminance transformation function to each of the pre-warped images to blend colors in the tiled display images further comprising:
applying an inverse of the spatial-luminance transformation function to each of the pre-warped images;
de-normalizing each of the applied pre-warped images; and
applying a look-up table to each of the de-normalized images to provide a second transformed input video signal to each of the one or more projectors, respectively.
25. A method of reducing one or more undesirable characteristics in a tiled display system, comprising:
generating an image of a predetermined dot pattern;
displaying the generated image of the predetermined dot pattern on to a screen using a projector including a spatial filter to modulate light to produce a seamless tiled display;
capturing the displayed image of the predetermined dot pattern using a camera;
comparing the captured predetermined dot pattern with a predetermined expected dot pattern to determine whether the formed predetermined dot pattern has the one or more undesirable projector characteristics;
generating a display-to-screen spatial transformation function that can be applied to an input video signal of the projector to reduce the undesirable projector characteristics; and
processing the input video signal using the display-to-screen spatial transformation function to provide a first transformed input video signal such that the one or more undesirable projector characteristics are reduced.
26. The method of claim 25, wherein comparing the captured predetermined dot pattern with a predetermined expected dot pattern further comprising:
calculating dot locations by subtracting a black captured image from the captured image; and
sorting the calculated dot locations with known dot locations of the predetermined expected dot pattern.
27. The method of claim 26, wherein generating the display-to-screen spatial transformation function comprises generating the display-to-screen spatial transformation function based on an outcome of sorting the calculated dot locations with the known dot locations.
28. A seamless tiled display system, comprising:
a spatial filter including a spatial gradient profile disposed in an image path between each of multiple projectors and a screen, respectively to produce a seamless tiled display;
a camera for capturing a displayed subset of a first predetermined image by each of the multiple projectors; and
a tiled display processor, coupled to each of the multiple projectors and the camera, wherein the tiled display processor further comprises:
an analyzer to generate the rest of the first predetermined image that is not displayed due to the disposition of the spatial filter in the image path between the projector and the screen, wherein the analyzer combines the generated first predetermined image with the captured subset of the first predetermined image to form a composite of the first predetermined image, wherein the analyzer determines whether the formed composite first predetermined image has one or more undesirable projector characteristics, and the analyzer further
identifies a display-to-screen spatial transformation function that can be applied to an input video signal of the projector to reduce the undesirable projector characteristics; and
processes the input video signal using the identified display-to-screen spatial transformation function to provide a first transformed input video signal such that the one or more undesirable projector characteristics are reduced.
29. The system of claim 28, wherein the processor further comprises a comparator coupled to the analyzer to receive the formed composite of the first predetermined image from the analyzer and to compare the received formed composite of the first predetermined image with a predetermined expectation to determine whether the formed composite of the first predetermined image has the one or more undesirable projector characteristics.
30. The system of claim 28, wherein the first predetermined image is a dot pattern.
31. The system of claim 28, wherein the analyzer generates the rest of the first predetermined image using an extrapolation function.
32. The system of claim 31, wherein the extrapolation function comprises a least squares fit of a polynomial function.
33. The system of claim 32, wherein the extrapolation function is selected from the group consisting of a quadratic or a higher order polynomial function and a cubic-spline function.
34. The system of claim 28, wherein the analyzer further
displays flat field images of varying intensities using the projector, and the camera captures the displayed flat field images of varying intensities;
normalizes the captured flat field images with respect to a highest gray scale flat field image and a lowest gray scale flat field image and determines a gamma-corrected linearized luminance at a center of the displayed flat field images of varying intensities, and further normalizes the flat field images with the determined gamma-corrected linearized luminance at the center of the displayed flat field images of varying intensities; and
identifies a spatial function that can be applied to simulate each of the normalized flat field images and determines a spatial-luminance transformation function using the spatial function for providing an effective color calibration.
35. The system of claim 34, wherein the analyzer
determines the spatial-luminance transformation function by applying spatial function to predetermined sections of each of the flat field images;
determines a first set of coefficients of the spatial function for each of the flat field images, and further identifies the spatial-luminance transformation function that can simulate the determined first set of coefficients for each section of the predetermined section of the normalized flat field images; and
determines a second set of coefficients for the first set of coefficients that will effectively blend colors in the tiled displays.
36. The system of claim 35, wherein the spatial function is a local bilinear function.
37. The system of claim 36, wherein the spatial-luminance transformation function is a quadratic or a higher order polynomial function.
38. The system of claim 36, wherein the flat field images of varying intensities comprises flat field images of monochrome, red, green and blue colors of varying gray scales.
39. The system of claim 36, wherein the tiled display processor further comprises a memory, coupled to the analyzer and the comparator, to store gamma-corrected linearized luminance at the center of the displayed flat field images of varying intensities and a look-up-table for the spatial-luminance transformation function.
40. The system of claim 36, wherein the projector further displays a predetermined template on to the screen, the camera further captures an image of the displayed predetermined template, and the analyzer further determines whether the captured image has one or more undesirable camera characteristics, and generates a screen-to-camera spatial transformation function to reduce the one or more undesirable camera characteristics.
41. The system of claim 40, wherein the analyzer applies the screen-to-camera spatial transformation function to the captured subset of the first predetermined image to reduce the one or more undesirable camera characteristics.
42. The system of claim 40, wherein the predetermined template is a dot pattern.
43. The system of claim 40, wherein the analyzer
segments a high-resolution image into tiled images based on an array of displayed images and regions of overlap between the arrays of displayed images of the tiled system;
pre-warps each of the segmented tiled images; and
applies the spatial-luminance transformation function to each of the pre-warped tiled images to effectively blend colors in the tiled displays.
44. The system of claim 43, wherein the analyzer further
segments the high-resolution image into the tiled displays by adding a predetermined overlapping region to each of the segmented tiled images; and
applies a ramping function to the overlapping region of each of the segmented tiled images to ensure a correct proportion of color luminance mix in the overlapping region.
45. The seamless tiled display system of claim 43, wherein the analyzer further pre-warps each of the segmented tiled images by processing each of the segmented tiled images using the display-to-screen spatial transformation function to provide a first transformed input video signal such that the one or more undesirable projector characteristics are reduced.
46. The seamless tiled display system of claim 45, wherein the analyzer further
applies an inverse of the spatial-luminance transformation function to each of the pre-warped images;
de-normalizes each of the applied pre-warped images; and
applies a look-up table to each of the de-normalized images before inputting each of the images into the one or more projectors to blend colors in the tiled display images.
Description

The invention described herein was made in the performance of work under NASA Contract NAS 1-20219, and is subject to the provisions of Section 305 of the National Aeronautics and Space Act of 1958 (42 U.S.C. 2457). The government may have certain rights in the invention.

FIELD OF THE INVENTION

This invention relates generally to the field of optical displays, and more particularly pertains to calibrating tiled displays using multiple projectors to produce a large, and/or a higher resolution image.

BACKGROUND

Multiple projection displays have been proposed and used for many years. In the 950's, the “CINERAMA” system was developed for the film industry. The CINERAMA system used three films to project three images using three separate projectors, which were then combined to form a single panoramic image. Disneyland continues to use a similar multiple projector system, wherein a circle of projectors shine onto a screen that circles the wall of a round room.

In the video field, multiple projector systems have been proposed and used for a number of specialty applications. U.S. Pat. No. 4,103,435 to Herndon and U.S. Pat. No. 3,833,764 to Taylor suggest using multiple projector systems for flight simulators. In many of these systems, multiple video screens are placed next to each other to form a large tiled image display.

A difficulty with many of the video based multiple projector display systems is that the multiple images often do not appear as one single continuous image on the display screen. When multiple images are projected side-by-side and/or top-to-bottom on a single screen, there is normally a seam or overlapping region between the images for example, an M×N projector array, where M and N are generally expressed as positive integer values, though, in using overlap and portions of displays, fractional values may be assigned. Also M×N projector arrays can be arranged to have constant and identical overlap or can be arranged to have varying degrees of overlap, depending on one's optimization criteria, which can include reliability, fault tolerance, cost and performance. The final display image will either appear as multiple images placed side-by-side with a gap between images or, if the images are made to overlap on a single screen, with a bright line or band there between. In the region of overlap the light from each projector will add to the output light of the other. This applies to the black output level as well. Ideally, when displaying a black image, this region of overlap should be generally uniformly black across the entire displayed image. Instead one generally observes the black image to brighten in the regions of overlap. When the images of two projectors overlap, the amount of light in the overlapped regions of the images is approximately double the amount of light observed on the screen in regions where only a single projector image resides; in regions where four projected images overlap, the amount of light is approximately four times that of the single projector image, and so on. Thus, the observer of the screen will generally see the output image containing objectionable artifacts. The same effects happen for white images, and for all images in between black and white. Generally, the black and the white images may be conceptualized as the upper and lower reference levels for constructing any image whose content spans these two extremes.

The prior art, for example, in the Panoram tiled display resolved overlap issues by requiring the display device to have a black reference level having very low stray light. This needed CRTs, because CRTs have huge native contrast ratios and deep black, several times darker than other common display media such as LCD projectors and DMD projectors. While the deep-dark display or CRT-only architecture might work well for many applications, it fails to meet requirements found in the cinematic, medical and other industries demanding high image quality and performance. In these high performance applications, the contrast ratio requirements often exceed 1000:1. The cinema industry generally requires 1500:1, and the medical industry generally requires displays for digital radiography having contrast ratios in the range of about 2000:1 to 4000:1. With the contrast ratio of CRTs at that or a lesser range, any overlapping strategy as used in the CRT-only architecture fails. It divides the contrast ratio by the number of CRTs used. Thus, for a cinematic application requiring a contrast ratio of 1500:1, any overlap of the CRTs will shrink the contrast ratio to 750:1 in the region of overlap. Any regions having four CRTs overlapping in a 2×2 matrix, will show a quadrupling in brightness and thus a reduction in contrast ratio to a mere 375:1. This is observable and generally objectionable in the industry.

Attempts have been made to hide such artifacts, one such example being raising the regions of non-overlap to the same brightness levels as the regions of overlap. Such practices are usually implemented by adjusting the input video level to obliterate the visibility of the regions of overlap. However, this method reduces the contrast ratio over the entire display, even in areas where only a single projector projects its image content. And in cases where multiple CRTs or other imaging devices overlap their imagery, the contrast ratio over the entire display will be compromised accordingly.

What is desired is a fall-off in intensity of black and white levels such that the superposed images produce a uniform luminance from center to edges, including the overlapped regions of the projected image. In practice, such an ideal luminance profile is difficult to achieve, as the displays generally exhibit a fall-off in intensity from the center of a displayed image to its edges. To attain a uniform, center to edge luminance profile requires clipping the display's native intensity at display center and elsewhere to the same value as at the edges. Unfortunately, this will result in the loss of the display's native brightness and will significantly reduce the power to image brightness conversion efficiency of the system. Another method based on insensitivity of human vision to low spatial frequency changes is to allow a fall-off of the luminance profile near the edges of the tiled image. In theory, such profiles can be achieved electronically by adjusting the video going into each display. The corrective functions can be multiplied by the image content and will result in a uniform output over much of the gray scales to be rendered. However, the closer the input image approaches the black state, the more the actual deviates from the ideal using this method. This is because the input video commanding a black state on the display does not achieve a true black state in practice. This, as was explained above, is because display technologies generally pass or emit light even when displaying black.

To overcome the limitations described above, a pending commonly assigned patent application to Chen et al, suggest using an optical function generator to generate a spatial gradient profile, then to apply the spatial gradient profile to a spatial filter and then to dispose the spatial filter anywhere in an image formation path of each of the displays to produce a seamless tiled display image.

Generally, tiled displays require periodic re-calibration because the performance of their projectors and/or other hardware tend to change over time. To overcome this problem commonly assigned pending patent applications to Chen et al, suggest a method and apparatus to calibrate tiled displays not including spatial filters in their projectors. However, the method and apparatus disclosed in the pending patent application does not lend itself to calibrate the tiled displays including spatial filters in their projectors because the spatial filters generally change the luminance characteristics around the edges of the display. This can affect the displaying of a template used in the calibration process. Therefore, there is a need in the art for a method and apparatus to calibrate tiled displays including spatial filters in their projectors.

Also, the pending patent applications disclose a method and apparatus that requires a lot of memory and hardware to calibrate the tiled displays. Therefore, there is also a need in the art for a method and apparatus that requires less memory, less hardware, and has an improved processing speed to produce a high-resolution tiled image.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a method of calibrating a seamless tiled display image having multiple overlapping discrete images produced by multiple displays generates a display-to-screen spatial transformation function to reduce one or more undesirable geometric projector characteristics, for each of the projectors used in the tiled display. The method generates a screen-to-camera spatial transformation function to reduce one or more undesirable geometric camera characteristics for each of the cameras used in capturing the displayed images. The method requires generating a spatial luminance transformation function for effective color calibration for each of the display images in the tiled display. The method further requires inputting a high-resolution image into a tiled display processor to form the tiled images of the tiled display, and segmenting the inputted high-resolution image to form tiled images based on an array of images used in the tiled display. The method requires pre-warping the segmented tiled images using the display-to-screen spatial transformation function to reduce the one or more undesirable geometric projector characteristics. The method requires applying an inverse of the spatial-luminance transformation function to each of the pre-warped images to effectively blend colors in the tiled display images.

Other aspects of the invention will be apparent on reading the following detailed description of the invention and viewing the drawings that form a part thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a tiled display system used to calibrate and generate a two by two array of images according to the present invention.

FIG. 2 illustrates a flow diagram of an electronic calibration process for a seamless tiled display system according to the present invention.

FIG. 3 illustrates a flow diagram of generating a screen-to-camera spatial transformation function according to the present invention.

FIG. 4 illustrates a flow diagram of generating a display-to-screen spatial transformation function according to the present invention.

FIG. 5 illustrates a flow diagram of generating a spatial-luminance transformation function according to the present invention.

FIG. 6 illustrates a nine by nine dot pattern used in geometric distortion calibration.

FIG. 7 illustrates a resulting dot pattern when using a spatial filter in an image formation path of the display.

FIG. 8 illustrates one embodiment of a block diagram of a tiled display processor used in the system of FIG. 1.

FIG. 9 is a block diagram illustrating the calibration process according to the present invention.

DETAILED DESCRIPTION

In the following detailed description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that the embodiments may be combined, or that other embodiments may be utilized and that structural, logical and electrical changes may be made without departing from the spirit and scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims and their equivalents.

This document describes, among other things, a method and an apparatus for performing an electronic calibration on a tiled display system to reduce geometric distortion between screen-to-camera and projector-to-screen and color distortion to effectively blend colors in the display images of the tiled display.

FIG. 1 is a schematic diagram illustrating generally by way of example, but not by way of limitation, one embodiment of a tiled display system 100 according to the present invention. System 100 includes a two-by-two array of projectors 120 projecting images on to a display screen 110. Each of the two-by-two arrays of projectors 120 includes a spatial filter 160 to produce a seamless tiled display image on to the screen 110. The spatial filter 160 includes a spatial gradient profile to produce a seamless tiled display image. Spatial filter 160 can be disposed anywhere in an image formation path between each of the two-by-two array of projectors 120 and the screen 110. A camera 130 is coupled to a tiled display processor 140. In one embodiment, camera 130 can be one or more cameras.

In the system 100 shown in FIG. 1, the projectors 120 are arranged so that the images displayed on the screen have roughly similar size, overlap 150 and minimal spatial distortion. Generally, this manual coarse adjustment is quick and easy. In order to achieve a seamless tiled display image, each image has to be further calibrated before the images are sent to two-by-two array of projectors 120. This calibration is generally a fine adjustment to the projectors 120 and the camera 130. This is generally accomplished by doing an electronic calibration on the projectors 120, screen 110 and the camera 130. The purpose of the electronic calibration is to align the tiled images on the screen 110, blend tiled images seamlessly from one tiled image to another tiled image, and to reduce any luminance and chrominance variations inevitably left behind by the coarse manual adjustment. Although, it is possible to partially calibrate the tiled display system 100 by modifying optical components in each of the projectors 120, it is generally subject to time, temperature and other variations, making the coarse manual adjustment process impractical to implement. The tiled display system 100 shown in FIG. 1, automatically calibrates, controls and provides a seamless tiled display using image processing techniques described below.

FIG. 2 is a flow diagram illustrating generally a method 200 of doing an electronic calibration on a tiled display system to produce a seamless tiled display image. Method 200 includes determining a screen-to-camera spatial transformation function 210. FIG. 3 illustrates one method 210 of determining a screen-to-camera spatial transformation function. Method 210 includes displaying a predetermined template on to the screen 310. Displaying the predetermined template can include disposing a physical predetermined template on to the screen. Alternatively, displaying the predetermined template can be achieved by generating the predetermined template by the tiled display processor and displaying on the screen. In this embodiment, the predetermined template is a dot pattern such as a 9×9 dot pattern 600 as shown in FIG. 6. The next steps 320 and 330 include capturing the image of the displayed predetermined template using a camera and determining to see whether the captured image has one or more undesirable camera characteristics. The step of determining to see whether the captured image has one or more undesirable camera characteristics further includes comparing the captured image to a predetermined expected template to determine whether the captured image has the one or more undesirable characteristics. The next step 340 can include removing the predetermined template from the screen. The next step 350 includes generating a screen-to-camera spatial transformation function that can be applied to a captured image of the tiled display to reduce the one or more undesirable camera characteristics.

Step 220 in the process 200 determines a display-to-screen spatial transformation function using the previously determined screen-to-camera spatial transformation function 210. FIG. 4 illustrates one method 220 of determining the display-to-screen spatial transformation function. The method 220 includes disposing a spatial filter anywhere in an image path between the projector and the screen to modulate light to produce the seamless tiled display 410. The next step 420 includes displaying a subset of a first predetermined image on to a screen using a projector. The projector can be one or more projectors and the camera can be one or more cameras. In this example, the first predetermined image is a predetermined dot pattern such as a 9×9 dot pattern 600 shown in FIG. 6. The subset of the first predetermined image can be a 7×7 dot pattern 700 shown in FIG. 7. This is due to the application of a spatial luminance profile on to the spatial filter to produce a seamless tiled display. The next step can include applying the screen-to-camera spatial transformation function to correct the captured image for screen-to-camera geometric. The next step 430 includes capturing the partially displayed first predetermined image using a camera. The next step 440 includes generating the rest of the first predetermined image not displayed on the screen due to the inclusion of the spatial filter between the projector and the screen. Generating the rest of the first predetermined image can include using an extrapolation function to generate edge dots of the 9×9 dot pattern not displayed due to the spatial filter in the image path between the projector and the screen. The extrapolating function can be a least squares fit of a polynomial function. The extrapolating function to generate the edge dots can be based on functions such as a quadratic or a higher order polynomial function, or a cubic-spline function. The captured subset of the first predetermined image is then combined with the generated portion of the rest of the predetermined image to form a composite of the first predetermined image 450. The next step 460 includes determining whether the formed composite of the first predetermined image has one or more undesirable projector characteristics by comparing the formed first predetermined image with a predetermined expectation. In some embodiments, comparing the formed first predetermined image with a predetermined expectation includes calculating dot locations by subtracting a black captured image from a captured image and sorting the calculated dots with known locations of the predetermined expected dot pattern. The next step 470 includes generating a display-to-screen spatial transformation function that can be applied to an input video signal of the projector to reduce the undesirable projector characteristics. The input video signal is processed using the display-to-screen spatial transformation function to provide a first transformed input video signal to reduce the one or more undesirable projector characteristics. The steps of capturing, determining and processing can be repeated periodically.

The next step 230 in the process 200 is to determine a spatial luminance transformation function for providing an effective color calibration. FIG. 5 illustrates one method 230 of determining the spatial luminance transformation function. The method 230 includes the step 510 of sequentially displaying flat field images of varying intensities using the each of the projectors used in the tiled display system. Sequentially displaying flat field images includes displaying flat field images in red, green and blue primary colors with different gray scales. In another embodiment, sequentially displaying flat field images of varying intensities further defines gray scale levels of flat field images of varying intensities, and inputting signal that correspond to the defined gray scale levels of the flat field images of varying intensities. The next steps 520 and 530 in determining the spatial luminance transformation function include capturing displayed flat field images of varying intensities using the camera used in the tiled display system, and normalizing the captured flat field images with respect to the highest and lowest flat field images. The captured flat field images of varying intensities can be corrected for screen-to-camera distortion by applying the screen-to-camera spatial transformation function. Normalizing the captured flat field images can further include geometrically warping back the flat field images to a rectangular coordinate system using the display-to-screen spatial transformation function, with a camera measured luminance as L(x,y) at a pixel position x and y. The gray level and the camera luminance are normalized with respect to their highest and lowest values. In one embodiment, the highest and lowest gray scale values are 255 and 0, respectively. The camera luminance is normalized as L _ ( x , y ) = L ( x , y ) - L min ( x , y ) L max ( x , y ) - L min ( x , y )

where Lmax(x,y) and Lmin(x,y) are the luminance captured at Dref=255 and 0. The normalization process simplifies the algorithm and can accommodate a simpler hardware design for different color depths such as 24 or 30 bits. The normalization also separates fast varying components such as a light source, a light integrator or a condenser from slowly varying components such as non-uniform light valve transmission and the projector optical system.

The next steps 540 and 550 include determining a gamma-corrected linearized luminance at a center of the displayed flat field images of varying intensities, and normalizing the flat field images with the gamma-corrected linearized luminance at the center of the displayed flat field images of varying intensities by computing the reference gray level as {overscore (L)}ref, center=Scenter({overscore (D)}ref)={overscore (D)}′ref, where {overscore (D)}′ref is the reference gray level in gamma corrected space and Scenter −1({overscore (D)}′ref)={overscore (D)}ref is the inverse function that is applied to transform the image from the gamma-corrected space to the original space. The inverse gamma function is usually represented as discrete values, for example, eight or ten bit depth for each of the red, green, and blue colors. The input {overscore (D)}′ref and corresponding output Dref values in discrete format are implemented in the hardware as a look-up-table for the gamma correction function to simplify the hardware implementation. Generally, it is difficult to do an inverse of a mathematical function such as the one described above using hardware. The use of a table simplifies the hardware design and implementation. The input and output discrete values can be stored in the memory. Although the {overscore (L)}(x,y) is linearized at the center position with respect to {overscore (D)}′ref, the same gamma transformation function at the center position of the tile Scenter do not linearize other positions, i.e. {overscore (L)}ref(x,y)=Sx,y({overscore (D)}′ref)=Sx,y(Sc −1({overscore (D)}′ref))=tx,y({overscore (D)}′ref). In other words, Sx,ySc −1=tx,y≠1, where Sx,y is the gamma transformation function for the pixel position (x, y).

The next step 560 generates a spatial function that can be applied to simulate each of the normalized flat field images and determines the spatial luminance transformation function for providing an effective color calibration. The deviation of the gamma transformation function at off-center positions, tx,y, is usually a slowly-varying function and can be approximated by a linear combination of spatial functions L _ ( x , y ) = t x , y ( D _ ) = i = 0 m β i ( D _ ) f i ( x , y ) ,

where βi({overscore (D)}′) are the spatial coefficients for the corresponding functions fi(x, y). These spatial functions can be either global or local functions depending on the property of the projection system. In this embodiment, the spatial function is characterized as a local bilinear function L _ ( x , y ) = t x , y ( D _ ) = i = 0 m β i ( D _ ) f i ( x , y ) = β 0 ( D _ ) x + β 1 ( D _ ) y + β 2 ( D _ ) x y + β 3 ( D _ ) ,

where fo(x,y )=x, f1(x,y)=y, f2(x,y)=xy, f3(x, y)=1, and m=3. Further, the spatial coefficients βi({overscore (D)}′) can be represented as a linear combination of luminance functions. The next step 570 includes determining the spatial-luminance transformation function by characterizing luminance as a function of pixel position (x,y) and image digital value {overscore (D)}′. The spatial-luminance transformation function can be expressed analytically using a quadratic function as L _ ( x , y ) = t x , y ( D _ ) = j = 0 n ( i = 0 m c ij f i ( x , y ) ) ( D _ ) j ,

where cij are the spatial-luminance coefficients. The digital image value of {overscore (D)}′can then be derived as a standard quadratic function of luminance L at any pixel position (x, y). After the gamma correction with the aid of the table, the digital value D(x, y) is ready for use at the projectors. Other mathematical profiles other than quatratic, such as a higher order polynomial functions, can also be used to characterize the spatial-luminance transformation function.

Determining the spatial-luminance transformation function can further include applying the spatial function to predetermined sections of each of the flat field images, and determining a first set of coefficients (spatial coeffcients βi({overscore (D)}′)) of the spatial function for each of the predetermined sections of each of the flat field images and determining a second set of coefficinets (luminance coefficients cij) for the first set of coefficients that will effectively blend colors in the tiled displays.

Flat field images of varying intensities can include flat field images of monochrome, red, green and blue colors of varying gray scales. The varying intensities are chosen such that the luminance difference between two adjacent sampled intensities are small enough for the linear interpolation in between the varying intensities. Also in this embodiment, the highest and lowest flat field images means flat field images having a gray scale light intensity of 255 and 0, respectively.

The next step 240 in the process 200 includes inputting a high-resolution raw image into the tiled display system. Step 250 includes an adjustment performed on the input raw image. The adjustment segments the high-resolution image to form the tiled images based on the array of images in the tiled display and can further include adding a predetermined overlapping region to each of the segmented images. The next step can include applying a ramping function to the overlapping region of each of the segmented images to ensure a correct proportion of color luminance mix in the overlapping region. In a representative system, the high-resolution raw image has a resolution of 2560×2048 pixels and each of the four, segmented images have a resolution of 1280×1024 pixels.

The next step 260 in the process 200 includes pre-warping each of the segmented tiled images, including processing each of the segmented tiled images using the display-to-screen spatial transformation function to provide a first transformed input video signal to each of the projectors to reduce undesirable projector characteristics.

The next step 270 in the process 200 includes applying an inverse of the spatial-luminance transformation function to each of the pre-warped images to effectively blend the colors in the tiled display images. This can be done by de-normalizing each of the applied pre-warped images, and applying a look-up-table to each of the de-normalized images to provide a second transformed input video signal to each of the projectors.

FIG. 8 shows a block diagram of the tiled display processor 140, including major components and their interconnections to the projectors 120 and to cameras 130. Processor 140 includes an analyzer 810, a comparator 820, and a memory 830. The analyzer 810 includes an image compositor 840, an image warper 850, and an image blender 860. Also shown in FIG. 8, are the projectors 120 and the cameras 130 coupled to the tiled display processor 140.

FIG. 9 illustrates one embodiment of segmenting the raw input video signal. In this embodiment, the raw input video signal has a high-resolution of 2560×2048 pixels. In this embodiment the tiled display system 100 has a two-by-two array of tiles. In this embodiment, the analyzer 810 including the image compositor 840 segments the received high-resolution raw image into four images of a predetermined size before sending the segmented images to the respective projectors 120 for further processing. Each of the segmented images contains a certain overlap region 150 as shown in FIG. 1 (the overlap region 150 depends on a projector setup and a desired aspect-ratio arrangement). In the example embodiment shown in FIG. 9, each of the four segmented images has a resolution of 1280×1024 pixels projected by each of the four projectors 910. After segmenting, the image compositor 840 applies a ramping function to the overlap region 150 to ensure a correct proportion of color luminance mixes for each of the segmented images.

The image warper 850 receives the segmented images from the image compositor 840 and pre-warps each of the segmented images before sending the segmented images to the image blender 860 as shown in FIG. 9. Pre-warping is done to align pixels among the adjacent projectors 120, and to correct for optical or mechanical distortions among the projectors 120, the cameras 130 and the screen 110. In one embodiment, the image warper 850 pre-warps the received segmented images, by using a display-to-screen spatial transformation function to provide a first transformed input video signal such that the one or more undesirable projector characteristics are reduced as described in steps 240, 250, 260 and 270. The display-to-screen spatial transformation function is computed using a screen-to-camera spatial transformation function as outlined below.

Each of the projectors 120 displays a predetermined template on to the screen 110. In one embodiment, the predetermined template is a physical template posted on to the screen 110. In another embodiment, the predetermined template is generated by the tiled display processor 140 and projected by each of the projectors 120. Then the camera 130 captures an image of the displayed predetermined template. In one embodiment, the predetermined template is a predetermined dot pattern. In the example embodiment shown in FIG. 4, the predetermined dot pattern is a 9×9 dot pattern. Then the analyzer 810 determines whether the captured image has one or more undesirable camera characteristics. In one embodiment, the tiled display processor includes the comparator 820. In this embodiment, the comparator 820 compares the captured image with a predetermined expected template to determine whether the captured image has one or more undesirable camera characteristics such as key-stone, pin cushion, and barrel distortions. Then the analyzer 810 identifies a screen-to-camera spatial transformation function that can be applied to the input video signal of each of the projectors 120 to reduce the undesirable camera characteristics.

Each of the projectors 120 including the spatial filter 160 displays a subset of a first predetermined image on to the screen 110. Each of the cameras 130 is used to capture the displayed subset of the first predetermined image on the screen 110. Then the analyzer 810 analyzes and corrects the captured image for screen-to-camera geometric distortion by applying the screen-to-camera spatial transformation function as described in step 210. Then the analyzer 810 generates a display-to-screen spatial transformation function that can be applied to an input video signal of each of the projectors 120 to reduce the undesirable projector characteristics as described in step 220. Then the image warper 850 pre-warps the input video signal using the generated display-to-screen spatial transformation function to provide a first transformed input video signal to reduce the one or more undesirable projector characteristics.

The segmented and pre-warped image is then filtered through the image blender 860 using the spatial-luminance transformation function for proper color mixing via a search at each pixel position of each of the projectors 120. The spatial-luminance transformation function is computed using the color distortion calibration process as outlined in step 230. The image blending can be carried out in the following stages:1. Apply the inverse function of the spatial-luminance transformation function as D _ ( x , y ) = t x , y - 1 ( I input ( x , y ) 255 )

to the pre-warped first transformed input video signal. The slowly varying function of tx,y −1 allows sampling of the local bilinear functions at a much reduced resolution, such as 8×8, 16×16, or 32×32 blocks with the corresponding sets of local bilinear functions. Where Iinput is the input image of red, green, and blue colors.

2. Denormalize the digital value D′ with respect to the maximum D′max and minimum D′min luminance. D′max and D′min are the fast varying function and need much finer sampled resolution than tx,y −1 using

D′(x,y)={overscore (D)}′(x,y)×(D′ max(x,y)−D′ min( x,y))+D′ min(x,y).

Depending on the display characteristics, different sampling resolutions can be used. Blending usually requires full or close to full resolution to ensure a seamless image. With the disposition of the spatial filter 160 in each of the projectors 120, the requirement of close to full resolution is relaxed and a larger sampling period can be used.

3. Apply the look-up-table before feeding the image to the projectors 120 to effectively blend the colors in the tiled images using

I output(x,y)=255×S center −1(D′(x,y))

Where Ioutput is the output image of red, green, and blue colors.

The use of a table can be useful for LCD projectors because of steep transmission-voltage characteristics.

In the overlap region 150, the luminance ramps down smoothly and monotonically from one image to another during color blending. In one embodiment, approximately 80 pixels of overlap are used in the horizontal and vertical directions. Generally, color blending is easier to implement when more overlapping pixels are used. However, more overlapping pixels reduces effective resolution.

The tiled display processor 140 further includes a memory 830. Memory 830 is coupled to the analyzer 810 and comparator 820. In one embodiment, the memory 830 stores the display-to-screen and screen-to-camera transformation coefficients, spatial-luminance transformation coefficients, and the gamma-corrected linearized luminance at the center of the displayed flat field images of varying intensities.

Conclusion

The above described tiled display system provides, among other things, a method and apparatus to calibrate tiled displays including spatial filters in their projectors. Also the tiled display system simplifies the hardware and improves processing speeds.

The above description is intended to be illustrative, and not restrictive. Many other embodiments will be apparent to those of skill in the art. The scope of the invention should therefore be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US3833764Dec 14, 1972Sep 3, 1974Singer CoMultiple viewing surface display
US4103435Oct 8, 1976Aug 1, 1978The United States Of America As Represented By The Secretary Of The NavyHead trackable wide angle visual system
US5091773 *Oct 3, 1990Feb 25, 1992Thomson-CsfProcess and device for image display with automatic defect correction by feedback
US5136390Nov 5, 1990Aug 4, 1992Metavision CorporationAdjustable multiple image display smoothing method and apparatus
US5847784 *Jul 29, 1997Dec 8, 1998Hughes Electronics CorporationSelf adjusting tiled projector using test pattern and sensor
US5923789 *Aug 7, 1996Jul 13, 1999General Electric CompanyBand limited interpolation and projection of spatial 3-D images
US5956000 *May 12, 1997Sep 21, 1999Scitex Corporation Ltd.Digital image display system and method
US6151086 *Sep 14, 1999Nov 21, 2000Lambent LlcMethod and apparatus for controllably scattering light using birefringent liquid crystal
US6222593 *May 30, 1997Apr 24, 2001Olympus Optical Co. Ltd.Image projecting system
US6292171 *Mar 31, 1999Sep 18, 2001Seiko Epson CorporationMethod and apparatus for calibrating a computer-generated projected image
US6411302 *Jan 6, 1999Jun 25, 2002Concise Multimedia And Communications Inc.Method and apparatus for addressing multiple frame buffers
US6456339 *Oct 28, 1998Sep 24, 2002Massachusetts Institute Of TechnologySuper-resolution display
US6611241 *Nov 25, 1998Aug 26, 2003Sarnoff CorporationModular display system
JPH09326981A Title not available
WO1999014716A1Aug 24, 1998Mar 25, 1999Meir AloniElectro-optical display apparatus
WO1999031877A1Dec 12, 1997Jun 24, 1999Hitachi LtdMulti-projection image display device
WO2000018139A1Sep 23, 1999Mar 30, 2000Honeywell IncMethod and apparatus for calibrating a tiled display
Non-Patent Citations
Reference
1 *M. Hereld et al., "Introduction to Building Projection-based Tiled Display Systems," IEEE Computer Graphics and Applications, Jul./Aug. 2000, pp. 22-28.*
2Patent Abstracts of Japan, vol. 1998, No. 04, Mar. 31, 1998 & JP 09 326981 A (Olympus Optical Co Ltd), Dec. 16, 1997 Abstract and US 6 222 593 A (Higurashi et al) May 24, 2001.
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US7031547 *Mar 3, 2005Apr 18, 2006Nik Software, Inc.User definable image reference points
US7134080 *Aug 23, 2002Nov 7, 2006International Business Machines CorporationMethod and system for a user-following interface
US7215362 *Oct 30, 2003May 8, 2007Fraunhofer-Gesellschaft Zur Foerderung Der Angewandten Forschung E.V.Auto-calibration of multi-projector systems
US7245318 *Nov 1, 2002Jul 17, 2007Canon Kabushiki KaishaImaging apparatus that corrects an imbalance in output levels of image data
US7253841 *Apr 7, 2004Aug 7, 2007National Applied Research LaboratoriesRemote control method of tile display
US7306341 *Feb 28, 2005Dec 11, 2007Hewlett-Packard Development Company, L.P.Multi-projector geometric calibration
US7364304 *Mar 23, 2005Apr 29, 2008Seiko Epson CorporationProjector control
US7530019Sep 19, 2006May 5, 2009International Business Machines CorporationMethod and system for a user-following interface
US7589695 *May 21, 2003Sep 15, 2009Panasonic CorporationImage display apparatus, multidisplay apparatus, and brightness management apparatus
US7609444Oct 21, 2005Oct 27, 2009Hewlett-Packard Development Company, L.P.Projection partitioning and aligning
US7635188 *Jun 6, 2006Dec 22, 2009Barco Lighting Systems, Inc.Method and apparatus for creating a collage from a plurality of stage lights
US7663640 *Jul 2, 2004Feb 16, 2010The Trustees Of Columbia University In The City Of New YorkMethods and systems for compensating an image projected onto a surface having spatially varying photometric properties
US7703924Oct 25, 2005Apr 27, 2010The Trustees Of Columbia University In The City Of New YorkSystems and methods for displaying three-dimensional images
US7724205 *Dec 9, 2004May 25, 2010Seiko Epson CorporationImage display control method, apparatus for controlling image display, and program for controlling image display
US7859572Aug 6, 2007Dec 28, 2010Microsoft CorporationEnhancing digital images using secondary optical systems
US7868847 *May 24, 2005Jan 11, 2011Mark W MilesImmersive environments with multiple points of view
US7881563 *Feb 15, 2006Feb 1, 2011Nokia CorporationDistortion correction of images using hybrid interpolation technique
US7893393Apr 20, 2007Feb 22, 2011Mersive Technologies, Inc.System and method for calibrating an image projection system
US7901095Mar 27, 2009Mar 8, 2011Seiko Epson CorporationResolution scalable view projection
US7970233Aug 12, 2010Jun 28, 2011Nik Software, Inc.Distortion of digital images using spatial offsets from image reference points
US8063941Aug 6, 2007Nov 22, 2011Microsoft CorporationEnhancing digital images using secondary optical systems
US8064725Oct 10, 2009Nov 22, 2011Nik Software, Inc.Distortion of digital images using spatial offsets
US8102332Jul 21, 2009Jan 24, 2012Seiko Epson CorporationIntensity scaling for multi-projector displays
US8123360 *Jul 6, 2007Feb 28, 2012Seiko Epson CorporationMulti-projector composite image display system
US8130184Oct 21, 2005Mar 6, 2012Hewlett-Packard Development Company L. P.Image pixel transformation
US8152312 *Mar 5, 2007Apr 10, 2012Sony CorporationApparatus and method that present projection image
US8170377 *Nov 14, 2008May 1, 2012Canon Kabushiki KaishaImage processing apparatus, control method of image processing apparatus, program, and storage medium
US8189015 *May 11, 2006May 29, 2012Syndiant, Inc.Allocating memory on a spatial light modulator
US8195006 *Aug 2, 2005Jun 5, 2012Bauhaus-Universitaet WeimarMethod and device for representing a digital image on a surface which is non-trivial in terms of its geometry and photometry
US8218908 *Nov 1, 2007Jul 10, 2012Canon Kabushiki KaishaMixed content image compression with two edge data representations
US8253861 *Oct 20, 2005Aug 28, 2012Fujitsu Ten LimitedDisplay device, method of adjusting the image quality of the display device, device for adjusting the image quality and device for adjusting the contrast
US8269691Jun 26, 2009Sep 18, 2012Sony Computer Entertainment Inc.Networked computer graphics rendering system with multiple displays for displaying multiple viewing frustums
US8311366Jan 12, 2007Nov 13, 2012Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.System and method for calibrating and adjusting a projected image of a projection apparatus
US8368803 *Sep 10, 2009Feb 5, 2013Seiko Epson CorporationSetting exposure attributes for capturing calibration images
US8525752 *Dec 13, 2011Sep 3, 2013International Business Machines CorporationSystem and method for automatically adjusting electronic display settings
US8525753 *Mar 15, 2012Sep 3, 2013International Business Machines CorporationSystem and method for automatically adjusting electronic display settings
US8567953Apr 26, 2006Oct 29, 2013Imax CorporationSystems and methods for projecting composite images
US8589796Apr 3, 2008Nov 19, 2013International Business Machines CorporationMethod and system for a user-following interface
US8625925Oct 12, 2009Jan 7, 2014Google Inc.Distortion of digital images using spatial offsets from image reference points
US8777418Jan 26, 2006Jul 15, 2014Christie Digital Systems Usa, Inc.Calibration of a super-resolution display
US8803762Jun 3, 2013Aug 12, 2014International Business Machines CorporationSystem for automatically adjusting electronic display settings
US20090167949 *Mar 28, 2006Jul 2, 2009David Alan CasperMethod And Apparatus For Performing Edge Blending Using Production Switchers
US20090245661 *Nov 1, 2007Oct 1, 2009Canon Kabushiki KaishaMixed content image compression with two edge data representations
US20100328447 *Jun 26, 2009Dec 30, 2010Sony Computer Entertainment, Inc.Configuration of display and audio parameters for computer graphics rendering system having multiple displays
US20110058098 *Sep 10, 2009Mar 10, 2011Victor IvashinSetting Exposure Attributes for Capturing Calibration Images
US20110317937 *Jun 20, 2011Dec 29, 2011Sony CorporationInformation processing apparatus, information processing method, and program therefor
US20130057596 *Mar 29, 2011Mar 7, 2013Nec CorporationProjector, Projector System, and Image Correcting Method
US20130147684 *Dec 13, 2011Jun 13, 2013International Business Machines CorporationSystem and method for automatically adjusting electronic display settings
US20130147776 *Mar 15, 2012Jun 13, 2013International Business Machines CorporationSystem and method for automatically adjusting electronic display settings
WO2007085081A1 *Jan 25, 2007Aug 2, 2007Christie Digital Sys Ca IncCalibration of a super-resolution display
WO2007111589A1 *Mar 28, 2006Oct 4, 2007Thomson LicensingMethod and apparatus for performing edge blending using production switchers
WO2013159028A1 *Apr 19, 2013Oct 24, 2013Scalable Display Technologies, Inc.System and method of calibrating a display system free of variation in system input resolution
WO2014094077A1 *Dec 21, 2012Jun 26, 2014Barco NvAutomated measurement of differential latency between displays
Classifications
U.S. Classification382/254, 382/294, 348/745, 348/E05.144, 382/276, 348/E05.137, 348/E09.012, 348/E09.027, 382/275, 345/1.3, 382/284
International ClassificationH04N9/31, H04N9/12, H04N17/04, H04N5/74, G03B21/00, G09G5/00, G06T3/00
Cooperative ClassificationH04N9/12, H04N9/3147, H04N5/74, H04N9/3197, G06T3/4038, H04N9/3185
European ClassificationG06T3/40M, H04N9/31R3, H04N9/31S3, H04N9/12, H04N9/31V, H04N5/74
Legal Events
DateCodeEventDescription
Dec 4, 2012FPExpired due to failure to pay maintenance fee
Effective date: 20121012
Oct 12, 2012LAPSLapse for failure to pay maintenance fees
May 28, 2012REMIMaintenance fee reminder mailed
Mar 20, 2008FPAYFee payment
Year of fee payment: 4
Aug 30, 2000ASAssignment
Owner name: HONEYWELL INTERNATIONAL INC., NEW JERSEY
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:CHEN, CHUNG-JEN;REEL/FRAME:011060/0291
Effective date: 20000817